An attorney for 19 gay and lesbian Maryland residents urged the state's highest court yesterday to strike down a law banning same-sex marriage, saying there is "no constitutionally sufficient justification" for denying his clients and their children protections that only marriage affords.

During an hour-long argument in a crowded chamber of the Court of Appeals in Annapolis, attorney Kenneth Y. Choe of the American Civil Liberties Union invoked the civil rights struggle and said the ability to marry is a fundamental right that belongs to all Marylanders, not only to those for whom that right has always been recognized.

"Despite the fact that plaintiffs have formed committed relationships and loving households, the state excludes them and their children from the numerous important protections that come with marriage solely because the person whom they love is a person of the same sex," he said.

Assistant Attorney General Robert A. Zarnoch, the general assembly counsel, urged the court to let stand the statute that defines marriage as the union of a man and a woman. Arguing that the judiciary should defer to the legislature, Zarnoch noted that no federal or state appellate court in the country has held that, as the plaintiffs argue, there is a fundamental right to same-sex marriage.

"An invalidation of Maryland's law would have the unfortunate consequence of placing these issues outside the arena of public debate, outside the legislative and democratic process," Zarnoch said.

The court took the case after the state appealed a ruling by Baltimore Circuit Court Judge M. Brooke Murdock, who held in January that the 1973 law banning same-sex marriage is discriminatory and "cannot withstand constitutional challenge." In anticipation of an appeal, Murdock stayed her decision when she announced it.

With Murdock's ruling, Maryland was thrust into a debate that has raged across the country at least since 1996, when Congress passed a law barring federal recognition of same-sex marriages and allowing states to do the same.

Massachusetts alone recognizes same-sex marriage, but several states and the District allow domestic partnerships or civil unions that offer some of the rights of marriage.

Plaintiffs, activists on both sides and legal observers packed the wood-paneled courtroom in Annapolis yesterday in what was one of the court's most well-attended sessions in recent memory. The potential audience was wider still; the court began a webcast of its proceedings Thursday.

The judges asked few questions, and little hint of their leanings could be detected. Judge Dale R. Cathell was notably vocal during Choe's presentation, when he interjected questions five times -- once to ask whether in some instances the proper function of the court was, as Zarnoch had suggested, to defer to the legislature.

Later, on the steps of the courthouse, the legal abstractions faded as the plaintiffs described the protections they do not have because their relationships are not legally recognized: inheritance and adoption rights, decisions about life support, hospital visitation.

Patrick Wojahn, a disabilities lawyer, said his partner, Dave Kolesar, a broadcast engineer, had experimental brain surgery some time ago. Wojahn worried that he might not be able to ride in an ambulance if Kolesar's medical condition recurred and he had to be taken to a hospital.

"We just want to have the security to know that if something happens to him, or to me even, we will be able to be there for each other," Wojahn said.

Among those on the steps was RoseMarie Briggs of the Family Leader Network, a national lobbying organization that backs a constitutional amendment prohibiting same-sex marriage. She said children who are raised "in the home with their married mother and father in a low-conflict marriage" are more likely to succeed in school and to avoid such social hazards as illegal drug use.

"Our laws should reflect what is best for children, not what is best for adults," she said.

In court, Zarnoch argued that the disputed statute is "gender-neutral" because it does not benefit or burden one sex more than the other.

He also argued that gay men and lesbians do not constitute a "suspect class," a designation applied to racial minorities and other groups that have faced discrimination and are held to be deserving of special protections under the law.

Such classes, Zarnoch said, are typically politically powerless. By contrast, he said, "in Maryland, we have openly gay legislators who, in fact, are legislative powerhouses in leadership."

Choe disputed that, saying that if gay men and lesbians were politically powerful, they would have been able to achieve their aims through the legislature.